Modeling chemical equilibria, phase behavior, and transport properties in ionic liquid systems

A previously developed thermodynamic model for mixed-solvent electrolyte solutions and associated transport property models have been applied to calculating various properties of ionic liquid systems. For the analysis, imidazolium-based ionic liquids and their mixtures with water and organic solvents have been selected. The ionic liquids are treated as dissociable species that are subject to chemical speciation equilibria. The parameters of the model are determined from available thermodynamic property data including phase equilibria, activity coefficients, osmotic coefficients, enthalpies of mixing and dilution, and heat capacities. Subsequently, electrical conductivities and viscosities are calculated using the chemical speciation obtained from thermodynamic analysis. The modeling framework has been designed to reproduce the properties of ionic solutions at temperatures ranging from the freezing point to 300 °C and concentrations ranging from infinite dilution to the fused salt limit. The accuracy of the thermodynamic model has been verified by calculating vapor–liquid, liquid–liquid, and solid–liquid equilibria in wide ranges of composition and temperature. In view of the strong dependence of electrical conductivity and, secondarily, viscosity on the ionic concentration, the accurate representation of transport properties confirms that the thermodynamic speciation results are reasonable, thus verifying the applicability of the computational framework to modeling multiple thermophysical properties of ionic liquid systems.